1. Field of the Invention
The present invention relates to a process for tinting articles by ink jet printing, in particular optical and ophthalmic articles such as lenses for eyeglasses. The invention also relates to ink receptive coating compositions which can be used in such a process.
2. Description of Related Art
It is known in the ophthalmic art to tint lenses, coated or not, by dipping lenses into a liquid water based tinting bath maintained at a temperature around 95° C. during several minutes. Classical solutions used during this tinting process are commercially available BPI solutions.
For instance, U.S. Pat. No. 7,097,704 describes coating compositions comprising an additive R1-(OCH2CH2)n-O—R2 wherein at least one of R1 and R2 is a silane containing group represented by the formula:
with specified meanings for R3, R4, and x, n being a positive integer.
This additive is used in low amounts in the coating composition to enhance tintability, i.e. from 3% to a maximum of 9% by weight of the liquid coating composition.
Another tinting process is the ink jet printing. The advantage of this process is its fastness and its flexibility, allowing controlling the amount of tinting dye deposited on the article and to choose the area to be tinted on the article. Gradient of coloration can be obtained, as well as coloration pattern as desired.
The tinting composition is generally and preferably a water based solution.
When implementing ink jet printing, it is generally necessary to modify the surface of the article to receive the ink, typically by applying an ink receptive coating on the surface of the article. There are many requirements for the ink receptive coating.
The ink receptive coating has to provide a good resolution for any tinted pattern applied on it. The ink has to be firmly immobilized on/into the ink receptive coating, i.e. exhibit a good adhesion over time. It is preferred that the ink penetrates at least partially or completely the ink receptive coating.
The ink receptive coating may be a permanent coating or a temporary coating being used as a temporary support from which the dyes are transferred into the article. The dyes may be transferred in the substrate constituting the lenses or in a coating of the substrate, adjacent to the ink receptive coating.
Generally, the ink receptive coating composition comprises a hydrophilic polymer, along with a binder and/or additives. The hydrophilic polymer enhances compatibility with the water based ink and an inorganic colloid, such as colloidal silica confers porosity to the layer, so that the dyes more easily penetrate the ink receptive coating.
EP 199874 describes an ink jet recording sheet comprising a support and an ink receptive layer containing polyethylene oxide and a white filler.
The molecular weight of the polyethylene oxide used may range from 100,000 to 900,000 and preferably from 100,000 to 300,000. EP 199874 clearly mentions that polyethylene oxide does not provide sufficient binding strength to satisfy all requirements of a recording process. It is then preferred to include an additional resin in the composition to enhance the binding strength. No binder based on polymerizable silanes is described.
WO 01/18128 discloses a coating composition for lenses, containing partially hydrolyzed epoxyalkoxysilanes and a polyether surfactant that improves the tinting ability of the cured coating. The surfactant can be chosen from inert, non-reactive organosilicones containing a polyoxyalkylene group, which are free of hydrolyzable groups.
EP 2248865 discloses an antistatic sol/gel forming coating composition comprising at least one inorganic metal salt and a hydrolyzate resulting from the at least partial hydrolysis of compounds containing at least one polyalkylene oxide segment and at least one silicon atom bearing hydrolyzable groups. Said composition generates a cross-linked structure upon polymerization, and its dry extract contains less than 5% by weight of free polyalkylene oxide polymers.
JP 2000241601 describes a process for tinting plastic lenses comprising the following steps:                forming a coating on the surface of a plastic lens to be dyed, the coating comprising a water soluble polymer such as polyvinyl alcohol or polyethyleneglycol;        applying a solution containing disperse dye on the above coating;        heating to diffuse the disperse dye in the lens;        removing the coating by washing;        
US20080127432 describes a method for coloring an optical lens comprising the following stages:    a) preparation of a transparent printing primer comprising    (1) a binder composed of an aqueous dispersion of polymer, preferably an anionic polyurethane,    (2) an agent which enhances the diffusion of ink into the aqueous dispersion of polymer, said agent comprising a colloid; and/or    3) an agent which enhances the absorption of ink into the aqueous dispersion of polymer, said agent comprising an absorbent polymer, which might be a poly(alkylene) oxide;    b) deposition of the transparent printing primer;    c) drying the printing primer;    d) printing, using an ink jet printer, the printing primer covering the substrate and    e) drying the ink.
Preferably, the absorbent polymer is a polyvinyl alcohol. The amount of PVA is between 10 and 50% inclusive of the total weight of dry matter.
JP2005232273, JP2005220322, JP2004115597 and JP2004106328 disclose ink receptor layers for ink jet printing made of a polyurethane matrix which is further reacted with an alkoxylsilane bearing an isocyanate group.
All these ink receptor layers comprise alumina fine particles.
JP2009144089 describes tetraalkoxysilanes based coating materials for surface hydrophilization comprising tetraalkoxysilanes and/or their hydrolyzates, alkoxysilyl containing polyoxyethylenes (average molecular weight of polyoxyethylenes 400-2000, polyoxyethylene units content 40-75% and alkoxysilyl units content 15-40%), H20, and hydrophilic organic solvents. JP2009144089 does not relate to ink jet printing.
The ink receptive layers for ink jet tinting described in the prior art have several drawbacks.
The polyethyleneglycol, being not linked to the matrix, can soften or partially melt when the ink receptive layer is heated, implying homogeneity problems.
The presence of filler may increase the haze of the ink receptor coating.
An aim of the invention is to provide a novel process for tinting articles by ink jet printing.
Another aim is to provide a novel process for tinting articles by ink jet printing providing a more intense coloration than in the prior art, while preserving homogeneity of the tinting.
Another aim of the invention is provide a novel process for tinting articles which is simple to implement and provides a tinted article having a low level of haze, either the article is tinted or not, and a good resolution of pattern